1. Field of the Invention
The present invention relates to a substrate processing apparatus and an electrode structure, and more particularly to a substrate processing apparatus including an electrode structure which is connected to a high-frequency power supply and to a gas supply apparatus adapted to supply processing gas.
2. Description of the Related Art
As a substrate processing apparatus 60 adapted to perform plasma processing, for example, etching processing to a wafer W as a substrate, there is known, as shown in FIG. 6, an apparatus configured by including: a chamber 61 which houses the wafer W; a mounting stage 62 which is arranged in the chamber 61 and on which the wafer W is mounted; and a disc-like shower head 63 which is arranged opposite to the mounting stage 62, and which introduces processing gas into the chamber 61. In the substrate processing apparatus 60, high-frequency power supplies 64 and 65 are respectively connected to the mounting stage 62 and the shower head 63, which also function as electrodes. Then, the mounting stage 62 and the shower head 63 supply high-frequency power to the inside of the chamber 61, so that an electric field is generated in the chamber 61. The electric field generates plasma from the processing gas, so that the plasma performs plasma processing to the wafer W.
Meanwhile, in order to perform the plasma processing uniformly to the wafer W, it is necessary to make uniform the distribution of plasma density on the wafer W. However, in order to make uniform the distribution of plasma density, it is necessary to make uniform the distribution of the electric field. Thus, for example, as in the substrate processing apparatus 60, there has been developed a substrate processing apparatus 60 in which branching waveguides (power supply tubes) 66 connected to the high-frequency power supply 65 and connected to the shower head 63 symmetrically around the center of the shower head 63 are provided, to thereby make uniform the distribution of the electric field (for example, see Japanese Patent Laid-Open Publication No. 8-325759).
Further, the distribution of plasma density is influenced by the distribution of processing gas introduced from the shower head. Accordingly, it is known that as shown in FIG. 7, in an electrode structure 70 of the substrate processing apparatus, two mutually separated buffer chambers 72a and 72b are provided in a shower head 71, and a gas supply apparatus (not shown) for supplying processing gas is connected to each of the buffer chambers 72a and 72b via separate gas supply systems 73a and 73b, respectively, so as to control the flow rate of the processing gas in each of the gas supply systems 73a and 73b. In the electrode structure 70, each of the buffer chambers 72a and 72b is communicated with the inside of the chamber which houses a wafer, and the flow rate of the processing gas supplied to the inside of the buffer chambers 72a and 72b is controlled, so as to enable the shower head 71 to control the distribution of the processing gas introduced into the chamber.
Note that in the electrode structure 70, connecting sections 74a and 74b, which respectively connect the gas supply systems 73a and 73b to the buffer chambers 72a and 72b, are arranged at the same angle with respect to the center of the shower head 71, that is, in the same radial direction.
However, when the etching processing is performed to the wafer W by using the above described electrode structure 70 shown in FIG. 7, micro abnormal discharge (arcing) has been sometimes generated on the wafer W. Specifically, the arcing has been generated at the positions symmetrical with the positions at which the connecting sections 74a and 74b are arranged, with respect to the center of the shower head 71. The arcing may destroy a wiring and an insulating film of the semiconductor device which are formed on the wafer W, and hence it is necessary to prevent the generation of the arcing.